Often the number reads Zero on the Main Page, but when you click on your Globe there's you lives! Still intact. On rare occasions it reads Zero, you look and they are all gone, it's empty, but exit the game and re-enter and they show up again.

Unless you accidentally clicked "Accept" with all of them check-marked? Then they're gone...

If they were eaten by a bug? Hopefully FS can figure that out and fix it. Cheers!